Setting of imaging parameters using a scanner

ABSTRACT

A recording head ( 16 ) is operated to form a regular pattern of image swaths on a recording media ( 17 ). The regular pattern of image features comprises a first set of image features ( 60 A) that is formed with an imaging parameter set to a first predetermined value and a second set of image features ( 60 B) is formed with an imaging parameter set to a second predetermined value, different from the first predetermined value. Image features in the first set and the second set are arranged on the recording media with a sub-scan spatial frequency equal to a non-integer multiple of a sub-scan spatial frequency of the image swaths. A scanner ( 40 ) generates data ( 47 ) of the scanned pattern, wherein a first integer multiple of a sampling spatial frequency employed by the scanner is equal to a second integer multiple of the sub-scan spatial frequency of the first set and the second set of image features. The data is analyzed to determine a quantified value representative of banding between the first set of and the second set of image features are adjusted.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned copending U.S. patent applicationSer. No. ______ (Attorney Docket No. 95687/NAB), filed herewith,entitled IMPROVED SETTING OF IMAGING PARAMETERES, by Jackson et al., thedisclosure of which is incorporated herein.

FIELD OF THE INVENTION

The invention relates to the field of recording apparatus used to formimages on recording media. In particular, the invention relates tosetting imaging parameters of recording apparatus employed to formimages on recording media such as printing plates.

BACKGROUND OF THE INVENTION

Contact printing using high volume presses is commonly employed to printa large number of copies of an image. Contact printing presses employvarious printing elements such as printing plates, printing sleeves,printing cylinders, and the like to apply colorants to a surface to forman image thereon. The surface can form part of a receiver medium (e.g.paper) or can form part of an intermediate component adapted to transferthe colorant from its surface to the receiver medium (e.g. a blanketcylinder of a press). In either case, a colorant pattern is transferredto the receiver medium to form an image on the receiver medium.

These printing elements are a form of recording media that typicallyundergo various processes to render them in a suitable configuration foruse in a printing press. For example, exposure processes are used toform images on an imageable surface of a recording media that has beensuitably treated so as to be sensitive to light or heat radiation. Onetype of exposure process employs film masks. The masks are typicallyformed by exposing highly sensitive film media using a laser printerknown as an “image-setter.” The imaged film mask is placed in areacontact with a sensitized recording media, which is in turn exposedthrough the mask. Printing plates exposed in this manner are typicallyreferred to as “conventional printing plates.” Typical conventionallithographic printing plates are sensitive to radiation in theultraviolet region of the light spectrum.

Another conventional method exposes media directly through the use of aspecialized recording apparatus typically referred to as a plate-setter.A plate-setter in combination with a controller that receives andconditions image data for use by the plate-setter is commonly known as a“computer-to-plate” or “CTP” system. CTP systems offer a substantialadvantage over image-setters in that they eliminate film masks andassociated process variations associated therewith. Typically, arecording head within the CTP system is controlled in accordance withimage data to selectively emit radiation beams to form image pictureelements known as image pixels on a surface of a recording media. Theradiation beams typically induce a physical or chemical change to animage modifiable surface of the recording media.

Various factors can adversely affect the quality of the images formed onrecording media. This has led to a need for the establishment of variousprocess controls for the required image forming actions. Typically,there are a number of imaging parameters that need to be optimally setto achieve a desired quality result. One important parameter is thelevel of radiation exposure provided on the recording media. Exposure istypically defined as the amount of radiant energy per unit area thatimpinges on the recording media during the imaging process. Depending onthe recording media type, it may be necessary to control this parameterwithin a few percent or less.

This situation is further compounded in multi-beam recording apparatusin that each beam needs to impart a substantially equal exposure to therecording media so that various imaging errors or artifacts are notcreated. Unless it can be guaranteed that all beams in a multi-beamrecording head have identical size and propagation characteristics, itmay not be possible to perform a simple power or intensity balancebecause exposure has both a spatial component and a power or intensitycomponent. While it may be possible to directly measure beam size, themeasurement is quite complicated and accurate results are difficult toachieve. Systems exists which are well suited to beam analysis but theyare usually in the form of stand alone equipment and are not necessarilysuitable or cost effective for inclusion in a CTP system.

The pragmatic approach, which is commonly adopted, is to let therecoding media be the measurement tool. Since the human eye is sensitiveto slight image variations, a trained operator can sometimes make adiagnosis of an imaged recording media and perform the requiredadjustments to the recording apparatus based on these observations. Theuse of densitometers, which are instruments that determine the opticaldensity of an image element by measuring the intensity of radiationreflected or transmitted by the image element are sometimes alsoemployed.

Conventional methods for picking a best or optimum set-point for aparticular imaging parameter typically involve plotting a series ofimage strips, each of the image strips being formed in accordance with aparticular imaging parameter value. The optical density of each of theimage strips is measured using a densitometer and the imaging parametervalue corresponding to a particular optical density value is selected.Unfortunately, for many cases, the optical density varies only a littleas the imaging parameter value is varied and the accuracy of thedensitometer may be limited in detecting these subtle differences. Theseissues can make it very difficult to accurately set the particularimaging parameter to an optimum value.

Whether using a densitometer or simply judging a recording media by eye,the process remains manual and requires intervention of trainedpersonnel. As the use of recording apparatus such as CTP systems gainsin popularity, techniques that can be employed to conveniently adjustvarious imaging parameters for optimum performance become increasinglyimportant.

There is a need to provide improved methods and apparatus for setting upimaging parameters important in the process control of an image formingoperation undertaken on a recording media.

There is a further need to reduce operator intervention in an imageparameter set-up process, particularly with respect to making judgmentson the subjective quality of test patterns.

SUMMARY OF THE INVENTION

Briefly, according to one aspect of the present invention a method foradjusting an imaging parameter includes operating a recording head toform a regular pattern of image swaths while forming an image on arecording media; operating the recording head to form a regular patternof image features on the recording media, wherein the regular pattern ofimage features comprises a first set of image features that is formedwhile the imaging parameter is set to a first predetermined value and asecond set of image features that is formed while the imaging parameteris set to a second predetermined value that is different from the firstpredetermined value, and wherein the image features in each of the firstset of image features and the second set of image features are arrangedon the recording media with a sub-scan spatial frequency that is equalto a non-integer multiple of a sub-scan spatial frequency of the imageswaths in the regular pattern of image swaths; providing a scanneradapted to generate data while scanning over the regular pattern ofimage features formed on the recording media, wherein a first integermultiple of a sampling spatial frequency employed by the scanner duringthe scanning is equal to a second integer multiple of the sub-scanspatial frequency of each of the first set of image features and thesecond set of image features; analyzing the data to determine aquantified value representative of banding between the first set ofimage features and the second set of image features; and adjusting theimaging parameter based at least on the quantified value.

The invention and its objects and advantages will become more apparentin the detailed description of the preferred embodiment presented below.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments and applications of the invention are illustrated by theattached non-limiting drawings. The attached drawings are for purposesof illustrating the concepts of the invention and may not be to scale.

FIG. 1 is a schematic perspective view of an imaging and diagnosticsystem as per an example embodiment of the invention;

FIG. 2 is a flow chart representing a method as per an exampleembodiment of the invention;

FIG. 3A shows a calibration image that includes a plurality of imagefeature patterns formed on recording media as per an example embodimentof the invention;

FIG. 3B shows a detail A-A of a portion of one of the image featurepatterns shown in FIG. 3A;

FIG. 4 schematically shows a data arrangement generated by a scanneremployed to scan over a recording media imaged as per an exampleembodiment of the invention;

FIG. 5 is a block diagram representing a Fast Fourier Transform (FFT)algorithm employed in an example embodiment of the invention;

FIG. 6 shows an example of plot in the frequency domain created fromscanned data generated from an image feature pattern formed as per anexample embodiment of the invention;

FIG. 7 shows a distribution of various quantified values determined foreach of a plurality of different focus offset values according to anexample embodiment of the invention; and

FIG. 8 shows a distribution of quantified values determined for each ofa plurality of radiation source power levels according to an exampleembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the following description specific details are presented toprovide a more thorough understanding to persons skilled in the art.However, well-known elements may not have been shown or described indetail to avoid unnecessarily obscuring the disclosure. Accordingly, thedescription and drawings are to be regarded in an illustrative, ratherthan a restrictive sense.

FIG. 1 schematically shows an imaging and diagnostic system 100according to an example embodiment of the invention. Imaging anddiagnostic system 100 includes a recording apparatus 10 for forming animage 19 (i.e. schematically represented by broken lines) on a recordingmedia 17. Various images 19 can be formed by recording apparatus 10. Invarious example embodiments of the invention, various calibration imageswill be formed to determine a best set-point for a particular imagingparameter. Without limiting the scope of the possible images that can beformed, image 19 will herein be referred to as calibration image 19 forthe purpose of describing embodiments of the present invention.Recording media 17 can include various media comprising a surfacesuitable for forming calibration image 19 thereupon. Recording apparatus10 includes a media support 12, which in this example embodiment isconfigured as per an external drum configuration. Other embodiments ofthe invention can include other forms of media supports configuredaccording to internal drum configurations or flat-bed configurations forexample.

In this example embodiment, recording media 17 is supported on acylindrical surface 13 of media support 12. One or more edge portions ofrecording media 17 are secured to cylindrical surface 13 by clamps 28.Other example embodiments of the invention can secure recording media 17to media support 12 by other methods. For example, a surface ofrecording media 17 can be secured to cylindrical surface 13 by variousmethods including providing a low-pressure source between the surfaces.Media support 12 is movably coupled to support 20. In this exampleembodiment, media support 12 is rotationally coupled to support 20. Inthis example embodiment, media support 12 includes a plurality ofregistration features 25. Registration features 25 are employed toorient recording media 17 with respect to media support 12.

Recording apparatus 10 includes recording head 16, which is movablerelative to media support 12. In this example embodiment of theinvention, media support 12 is adapted to move by rotating about itsrotational axis. In this example embodiment, recording head 16 ismounted on movable carriage 18. Carriage 18 is operated to causerecording head 16 to be moved along a path aligned with the rotationalaxis of media support 12. Motion system 22 is employed to providerelative movement between recording head 16 and media support 12. Motionsystem 22 (which can include one or more motion systems) can include anysuitable drives needed for the required movement. In this exampleembodiment of the invention, motion system 22 is used to move mediasupport 12 along a path aligned with main-scan axis MSA and is used tomove recording head 16 along a path aligned with sub-scan axis SSA.Guide system 32 is used to guide carriage 18 which is moved under theinfluence of transmission member 33. In this example embodiment of theinvention, transmission member 33 includes a precision screw mechanism.In some example embodiments, a plurality of recording heads 16 is movedsuch that each of the recording heads 16 is moved independently of eachother. In some example embodiments, a plurality recording heads 16 aremoved in tandem.

Those skilled in the art will realize that various forms of relativemovement between recording head 16 and media support 12 can be used inaccordance with the present invention. For example, in some casesrecording head 16 can be stationary while media support 12 is moved. Inother cases, media support 12 is stationary and recording head 16 ismoved. In still other cases, both the recording head 16 and the mediasupport 12 are moved. One or both of recording head 16 and media support12 can reciprocate along corresponding paths. Separate motion systemscan also be used to operate different systems within recording apparatus10.

In this example embodiment, recording head 16 includes a radiationsource (not shown), such as a laser. The wavelength of radiation isselected to suit the type of recording media 17 that is being imaged andcan include wavelengths in the infrared, visible and ultravioletspectrums for example. In various example embodiments, recordingapparatus 10 includes a plurality of individually addressable recordingchannels 23, each of the recording channels 23 being controllable toform various image portions on recording media 17. The plurality ofrecording channels 23 can be arranged in different configurationsincluding one dimensional or two dimensional array configurations.

In this example embodiment, recording head 16 is controllable to emitvarious radiation beams 21 while scanning over recording media 17 toform calibration image 19. Radiation beams can be image-wise modulatedaccording to image data 37 specifying the image to be written. In thisexample embodiment, one or more of the recording channels 23 are drivenappropriately to produce radiation beams 21 with active intensity levelswherever it is desired to form an imaged portion of calibration image19. Recording channels 23 not corresponding to the imaged portions aredriven so as not to image corresponding regions. Each of the recordingchannels 23 is controllable to form a unit element of image typicallyreferred to as an image pixel or an image dot on recording media 17 inaccordance with information provided by image data 37. Various imagepixels can be combined with other image pixels to form various featuresof calibration image 19. In various example embodiments of theinvention, image pixels can be arranged in various image pixel patternsincluding halftone patterns, stochastic patterns and hybrid patterns forexample.

Calibration image 19 can be formed on recording media 17 by differentmethods. For example, recording media 17 can include a modifiablesurface, wherein a property or characteristic of the modifiable surfaceis changed when irradiated by a radiation beam 21. A radiation beam 21can be used to ablate a surface of recording media 17 to form acalibration image 19. A radiation beam 21 can be used to facilitate atransfer of an image forming material to a surface of recording media 17to form calibration image 19 (e.g. a thermal transfer process). Aradiation beam 21 can undergo a direct path from a radiation source tothe recording media 17 or can be deflected by one or more opticalelements towards the recording media 17.

In many cases, the number of recording channels 23 is insufficient tocompletely form calibration image 19 during a single marking operation.Accordingly, calibration image 19 can be formed by merging multiplesub-images together, each of the sub images being formed during acorresponding marking operation. The sub-images can be formed indifferent manners. For example, calibration image 19 can be formed fromplurality of markings referred to as “shots.” During each shot,recording head 16 is positioned relative to a region of recording media17. Once positioned, recording channels 23 are activated to form anarrangement of image pixels on the region of recording media 17. Oncethe arrangement of image pixels is formed, relative movement betweenrecording channels 23 and recording media 17 is effected to position therecording channels 23 in the vicinity of an adjacent region and anothershot is taken to form a next image pixel arrangement.

The various sub-images can also be formed by scanning. In some exampleembodiments of the invention, scanning can be performed by deflectingradiation beams emitted by recording channels 23 relative to recordingmedia 17. In some example embodiments, scanning can include establishingrelative movement between the recording channels 23 and recording media17 as the recording channels 23 are activated to form correspondingimage pixels. In these example embodiments, a column of image pixels isformed along a scan direction by a given recording channel 23 asrelative movement between the given recording channel 23 and therecording media 17 is established. Relative movement can include movingone or both of the recording channels 23 and recording media 17. Each ofthe scanned image pixel columns are combined to form a sub-imagetypically referred to as an image swath.

Different scanning techniques can be employed to form image swaths. Forexample, “circular” scanning techniques can be used to form “ring-like”or “circular” image swaths. A circular image swath can be formed whencontroller 30 causes recording head 16 to emit radiation beams 21 whilemaintaining recording head 16 at a first position along sub-scan axisSSA and while moving media support 12 along a direction of main-scanaxis MSA. In this regard, scanning occurs solely along a main-scandirection. After the completion of a first circular image swath,recording head 16 is moved to a second position along sub-scan axis SSA.A second circular image swath is then formed as recording head 16 isoperated to emit radiation beams 21 while maintaining recording head 16at second position and while moving media support 12 along a directionof main-scan axis MSA.

Helical scanning techniques can be employed to form helical image swathswhich are formed in a spiral or helical fashion over a surface ofrecording media 17. For example, helical image swaths can be formed whencontroller 30 causes recording head 16 to emit radiation beams whilesimultaneously causing recording head 16 to move along a direction ofsub-scan axis SSA and media support 12 to move along a direction ofmain-scan axis MSA. In this regard, scanning occurs along both amain-scan direction and along a sub-scan direction and each helicalimage swath comprises an orientation that is skewed relative tomain-scan axis MSA.

It is to be noted that other forms of skewed scanning techniques similarto helical scanning techniques can be used in various embodiments of thepresent invention. Skewed scanning techniques need not be limited toexternal drum configurations but can also be employed with otherconfigurations of recording apparatus. For example, in some internaldrum recording apparatus, media is positioned on a concave surface of amedia support while a radiation beam is directed towards an opticaldeflector positioned along a central axis of the media support. Theoptical deflector is rotated while moving along central axis to causethe radiation beam to follow a spiral path on the surface of therecording media. Flat-bed recording devices can include coordinatedmovement between the recording channels and the recording media to formvarious image swaths with a particularly desired orientation.

In some cases, the radiation beam 21 emitted by recording channels 23have a limited depth of focus and thus require focus adjustmentperiodically or in real time. In such systems, any significant driftwill take radiation beams 21 out of focus and adversely affect a desiredquality of an image. The effect can be quite pronounced and it is notuncommon for a drift of in the order of several microns to significantlydegrade imaging performance. Recording apparatus 10 can be equipped witha focus adjustment mechanism which can effect a simple focus adjustmentbetween plots in some example embodiments of the invention. In otherexample embodiments, the focus adjustment mechanism can include a servofocus controller which continuously adjusts to keep focus in a desiredrange. An example of a focus adjustment mechanism is contained incommonly assigned U.S. Pat. No. 6,137,580 (Gelbart), which is hereinincorporated by reference in its entirety. In this example embodiment,an auto-focus system 35 is employed. Auto-focus system 35 includes asecondary laser source 36 to generate an incident beam (not shown) on asurface and a position sensitive detector 38 to receive the reflectedbeam and detect the position of the surface. The secondary laser source36 can be at a wavelength different from that of the primary lasersource used in the generation of radiation beams 21. This has theadvantage of separating the auto-focus signals from the writing signalsto avoid crosstalk. Position sensitive detector 38 can include aphoto-detector, a CCD detector or any other detector that is suitablefor detecting a position of a reflected beam.

Imaging and diagnostic system 100 further includes a scanning imagesensor which in this example embodiment includes scanner 40. Scanningimage sensors which typically employ various image capture sensors areused to scan an image and generate data representing a portion of theimage that was scanned. Present day scanners typically employ a chargecoupled device (CCD) or a contact image sensor (CIS) as the imagecapture sensor. A typical CCD type scanner has at least one row ofphoto-elements for detecting the light intensity of a predeterminednumber of samples of an image that is to be scanned. The scanningresolution of a scanner is typically measured in dots per inch (DPI)which can vary from scanner to scanner. In many flatbed scanners, theresolution is determined by the number of sensors in a row of thesensors (i.e. typically referred to the X direction scanning rate) andby the sampling rate of the array along a scanning direction of thescanner (i.e. typically referred to as the Y direction scanning rate).For example, if the resolution is 300 DPI×300 DPI for a scanner that iscapable of scanning a letter-sized entity, then the scanner wouldtypically employ at least one row made up of 2550 sensors (i.e. 300DPI*8.5 inches) and would employ a drive suitable for conveying thesensor array in increments of 1/300th of an inch (i.e. the samplingspatial period) to produce the sampling spatial frequency of 300 cyclesper inch. In this example embodiment, scanner 40 includes a sensor array42 arranged along the X direction. Sensor array 42 is adapted togenerate data 47 during a scanning operation along the Y direction. Invarious example embodiments, data 47 is grayscale data. A limited numberof sensor elements are schematically shown in sensor array 42 forclarity and their illustrated number is not indicative of a scanningresolution of scanner 40.

In some example embodiments of the invention, scanner 40 is astand-alone device while in other embodiments scanner 40 is incorporatedinto some other sub-system in imaging and diagnostic system 100 such asrecording apparatus 10 by way of non-limiting example. In some exampleembodiments of the invention, scanner 40 is a flatbed scanner which canform the basis of an economic diagnostic tool. Although other imageacquisition and measurement devices can be employed, scanners aretypically preferred in some example embodiments because of their preciseregistration, consistent geometric scale, illumination uniformity andmassive parallel data acquisition capabilities. In example embodimentswhere a scanned image comprises color attributes, scanner 40 can includemultiple sensor arrays 42, with a particular color filter associatedwith each of the sensor arrays 42. In typical applications, red, greenand blue color filters are employed.

Imaging and diagnostic system 100 includes controller 30, which caninclude one or more individual controllers. Controller 30 can be used tocontrol one or more systems of recording apparatus 10 including, but notlimited to various motion systems 22 used by media support 12 andcarriage 18. Controller 30 can also control media handling mechanismsthat can initiate the loading or unloading of recording media 17 to, orfrom, media support 12 respectively. Controller 30 can also provideimage data 37 to recording channels 23 and control recording channels 23to form image pixels in accordance with this data. As shown in FIG. 1,scanned data 47 generated by scanner 40 is provided to controller 30.Controller 30 is operable for analyzing scanner data 47 in accordancewith various example embodiments of the invention. Various systems canbe controlled using various control signals or implementing variousmethods. Controller 30 is programmable and can be configured to executesuitable software and can include one or more data processors, togetherwith suitable hardware, including by way of non-limiting example:accessible memory, logic circuitry, drivers, amplifiers, A/D and D/Aconverters, input/output ports and the like. Controller 30 can comprise,without limitation, a microprocessor, a computer-on-a-chip, the CPU of acomputer or any other suitable microcontroller. Controller 30 canconsist of several different logical units, each of which is dedicatedto performing a particular task.

FIG. 2 depicts a flow diagram representing a method 200 according to anexample embodiment of the invention. Although method 200 is referencedto a use of imaging and diagnostic system 100, it is to be understoodthat is for illustration purposes only and does note preclude the use ofother suitable systems. Recording media 17 is appropriately mounted onmedia support 12 and calibration image 19 is formed on recording media17 in step 210. Calibration image 19 can comprise a number of imagedregions that are related to a particular imaging parameter that is to beoptimally set. An imaged region can include an image feature patternsuitable for the set-up of a particular imaging parameter. In someexample embodiments, calibration image 19 can include a plurality ofimaged regions, wherein at least one of the imaged regions correspondsto a different imaging parameter than another of the image regions. Insome example embodiments, calibration image 19 can include a pluralityof imaged regions, wherein each of the imaged regions is formed inresponse to a change in a particular parameter of an imaging process. Insome example embodiments, each of the image imaged regions is formed inresponse to a change in a selected parameter of an imaging process whileone or more other imaging parameters of the imaging process remainconstant. By way of non-limiting example, the an imaging parameter canbe selected to be any one of: a power of a radiation source ofassociated with recording head 16, an intensity of recording channels23, a speed of media support 12, a parameter related to the focusing ofradiation beams 21 or any one of a number of the parameters which haveand effect on an image formed by recording apparatus 10.

FIG. 3A shows a calibration image 19 comprising a plurality of imagefeature patterns 50 formed on recording media 17 as per an exampleembodiment of the invention. For clarity, recording media 17 is shown inan unwrapped or “flat” orientation. In this example embodiment, each ofthe image feature patterns 50 is formed by scanning radiation beams 21over recording media 17. Main-scan axis MSA and sub-scan axis SSA areadditionally shown to establish a reference frame for the image formingscans. In this example embodiment, recording media 17 and its associatedcalibration image 19 are appropriately sized in accordance with the sizelimitations of scanner 40. The number of image feature patterns 50formed is determined based on various factors. In particular, the totalnumber of image feature patterns 50 is selected in accordance with asubsequent analysis (i.e. to be described later) of the patterns todetermine an optimum imaging parameter value. The present inventors havedetermined that usually at least ten image feature patterns 50 arerequired to effectively see a performance trend associated with changesin the selected imaging parameter. The present inventors have alsodetermined that good results can be achieved if each of the imagefeature patterns 50 comprises a main-scan size that comprises themajority of the main-scan size of recording media 17. Imaging over mostof recording media 17 allows errors in a subsequent analysis of theimage patterns to be reduced.

Each of the image feature patterns 50 can include various image pixelpatterns. In particular, the present inventors have determined that atwo-by-two checkerboard image pixel pattern is very sensitive to imagingvariations which in turn can cause variations to show up dramatically onrecording media 17. In other example embodiments of the invention, eachof the image feature patterns 50 can include various patterns of lines,features, solids or other entities. In various example embodiments, eachimage feature pattern 50 can include a specific pattern of image pixelsselected in accordance with the particular imaging parameter that isbeing investigated. In this illustrated embodiment, each of the imagefeature patterns 50 is arranged in a linear array. In other exampleembodiments, the plurality of image feature patterns 50 can be arrangedin other arrangements including for example, various two dimensionalregular and non-regular arrangements.

Each of the various image feature patterns 50 is formed in accordancewith a different predetermined value of a particular imaging parameterthat is being investigated. In this example embodiment, each of theimage feature patterns 50 corresponds to a change in a focusing imagingparameter. In many cases, the imaging performance of a recordingapparatus 10 is strongly related to focus and it is often best to firstensure that the apparatus is optimally focused prior to calibratingother imaging parameters. In this particular example embodiment, each ofthe image feature patterns 50 is formed while a radiation source withinrecording head 16 is maintained at common radiation level suitable forthe imaging of recording media 17 and a focus parameter is varied foreach of the image feature patterns 50 by a predetermined amount. In thisexample embodiment, different focus values are provided by auto-focussystem 35.

In this example embodiment, each of the each of the image featurespatterns 50 corresponds to a one of an overall focus offset valueselected from within a range of −9 μm to +9 μm from a selected zerofocus value. The zero focus value can be selected in various ways. Forexample, the zero value can arbitrarily selected within a given focalrange of recording head 16 or a previously identified value can beselected. In this example embodiment, each of the overall focus valuesvaries in step sizes of 2 μm, which the present inventors have found toprovide sufficient granularity in the determination of a best focus. Itis understood that these values are exemplary in nature and othersuitable values can be readily employed by other example embodiments ofthe invention.

In this example embodiment, each of the image feature patterns 50 ismade up of a plurality of sets of image features, wherein each of theimage features in each of the sets is formed in accordance with adifferent predetermined focus value. In this example embodiment, each ofthe different predetermined focus values is selected such that anaverage of the focus values is equal to particular focus offset valueselected for the corresponding image feature pattern 50 that the sets ofimage features form part of. For example, as shown in the detailed viewA-A in FIG. 3B, the image feature pattern 50 corresponding to theoverall focus offset value of −9 μm (i.e. image feature pattern 50A) isformed from a first set of image features 60A formed in accordance witha first focus value of −15 μm (i.e. represented by Focus Value #1) and asecond set of image features 60B formed in accordance with a secondfocus value of −3 μm (i.e. represented by Focus Value #2). In the thisexample embodiment each of the first and second focus values aredifferent from one another, and in particular, are selected such that anaverage of the two is equal to a third predetermined value which is thetargeted focus offset value of −9 μm in this case. It is to be notedthat the other image feature patterns 50 are also formed in a similarfashion. For example, the image feature pattern 50 corresponding to the+7 μm overall focus offset value would be formed from a first set ofimage features formed in accordance with a first focus value of +1 μmand second set of image features formed in accordance with a secondfocus value of +13 μm (i.e. the average of the first and second valuesequaling +7 μm). In this example embodiment, a 12 μm spread separateseach of the first and second focus values corresponding to each of theimage feature patterns 50. Although the present inventors have foundthat 12 μm spread works well for imaging resolutions on the order of2400 DPI, other suitable values can be employed in other exampleembodiments of the invention. For example, the present inventors havefound that a spread of 48 μm between the first and second focus valuesworks particularly well for an imaging resolution of 1200 DPI. In thisexample embodiment, the image features in each of the first and secondsets of image features in each of the image feature patterns 50 are madeup of a two-by-two checkerboard image pixel pattern.

Many conventional methods of determining a set point for a particularimaging parameter have tried to directly quantify or qualify an opticaldensity of each of plurality of test images in which each of the testimages is formed in accordance with a particular value of the imagingparameter. In many cases however only subtle differences in the opticaldensity among the test images exists and thereby limits theeffectiveness these conventional direct measurement techniques.

The present invention alleviates the limitations associated withdirectly measuring an optical density corresponding to a given imagingparameter target value. In various example embodiments of the invention,each image feature pattern 50 includes a plurality of different imagesfeatures wherein each of the image features are formed in accordancewith a member of a set of different imaging parameter values that boundsa targeted value of the imaging parameter. Rather than directlymeasuring an optical density corresponding to the targeted value of theimaging parameter, a difference in the optical densities of each of theplurality of image features corresponding to a given image featurepattern 50 is determined to provide a relative measurement. If thetargeted value corresponds to an optimum set-point for the imagingparameter, and each of the bounding parameter values are equally spacedfrom the optimum set-point, then there will be little difference betweenthe measured optical densities corresponding to each of the boundingparameter values. If the targeted value becomes biased from the optimumset-point, then differences between the measured optical densitiescorresponding to the bounding parameter values will increase. Thesedensity differences will create an imaging artifact known as “banding.”

Banding is common image artifact that usually manifests itself asdensity variations at the merge point between adjacent sub-images (e.g.adjacent image swaths). In many cases, these banding artifacts repeatwith a period related to the spatial period of the sub-images. Thepresent invention purposely induces a banding type artifact within eachof the image feature patterns 50 to determine an optimal set-point ofthe given imaging parameter that is being analyzed. In this exampleembodiment, each image feature pattern 50 is formed in accordance with adifferent set of the first and second predetermined parameter values.Each of the first and second sets of predetermined parameter values areselected to cause an optical density difference between the first andsecond sets of image features in each of the image feature patterns 50to be different than an optical density difference between the first andsecond sets of image features in another of the image feature patterns50. Accordingly, different levels of banding will be associated withdifferent ones of the image feature patterns 50.

As shown if FIG. 3B, the first set of image features 60A and the secondset of image features 60B are formed on the recording media such thatthe image features are interleaved with one another. In this regard, theimage feature pattern 50 corresponding to these interleaved imagefeatures is referred to as an interleaved pattern of image features.Since each of the first set of image features 60A and the second set ofimage features 60B is formed in accordance with a different focus value,a banding pattern is created by optical density differences among theinterleaved image features. In this example embodiment, each of theimage features of the first set of image features 60A are contiguouslyarranged with various image features in the second set of image features60B. In various example embodiments, the first set of image features 60Ais formed separately from the second set of image features 60B. Forexample, two image features of the first set of image features 60A canbe formed during a first imaging of the recording media 17 (e.g. duringa first scan) and a image feature of the second set of image features60B can be formed between the two image features during a second imagingof recording media 17 (e.g. during a second scan). In other exampleembodiments of the invention, an image feature in the first set of imagefeatures 60A can be formed at the same time as an image feature in thesecond set of image features 60B. The manner in which image features ineach of the first and second sets of image features 60A and 60B isformed may be motivated by the way an imaging parameter value (i.e. afocus value in this case) can be altered in accordance with theparticular image feature that is to be formed.

In various example embodiments of the invention, the level of banding ineach of the image feature patterns 50 is analyzed in the frequencydomain. An analysis of various test patterns in the frequency domain isdescribed in commonly-assigned U.S. Patent Publication No. 2009/0066796(Karasyuk et al.) which is hereby incorporated by reference in itsentirety. One particular problem associated with analyzing an elementcorresponding to a specific frequency in the frequency domain is thatthe results are sensitive to noise in the data that is being analyzed.

In this example embodiment, the first set of image features 60A and thesecond set of image features 60B are each formed as a regular pattern ofimage features on recording media 17. In the illustrated embodiment,each image features in the first set of image features 60A and each ofthe image features in the second set of image features repeat along asub-scan direction with a spatial frequency of 1 cycle per 128 imagepixels which can also be expressed as 18.75 cycles per inch for a 2400DPI image pixel resolution. In this example embodiment, the spatialfrequency of the image features in each of the first and second sets ofimage features 60A and 60B is selected to reduce extraneous cyclic noisefactors which can complicate a future analysis in the frequency domain.One potential source of noise is the image swaths that the imagefeatures are formed in. As previously stated, a regular banding patterncan arise at the merge points between adjacent image swaths. If each ofthe first and second sets of image features 60A and 60B has a sub-scanspatial frequency that is a harmonic of the sub-scan spatial frequencyof the image swaths, harmonic interference can arise during a subsequentanalysis in the frequency domain. In this example embodiment, recordinghead 16 is operated to form a plurality of image swaths, each having asub-scan size equal to 224 image pixels and accordingly any bandingassociated with the image swaths will correspond to a spatial frequencyof 1 cycle per 224 image pixels or 10.71 cycles per inch for a 2400image pixel resolution. In this example embodiment, the sub-scan spatialfrequency of each of the first and second sets of image features 60A and60B was selected to equal a non-integer multiple of the sub-scan spatialfrequency of the image swaths. In this example embodiment, the sub-scanspatial frequency of each of the first and second sets of image features60A and 60B was selected to not be a harmonic of the sub-scan spatialfrequency of the image swaths. In other example embodiments of theinvention, the sub-scan spatial frequency of the image swaths can beselected to equal a non-integer multiple of the sub-scan spatialfrequency of each of the first and second sets of image features 60A and60B. In other example embodiments, the sub-scan spatial frequency of theimage swaths can be selected to not be a harmonic of the sub-scanspatial frequency of each of the first and second sets of image features60A and 60B. The choice in which the sub-scan spatial frequency of eachof the first and second sets of image features 60A and 60B is selectedto equal an non-integer multiple or a non-integer factor of the sub-scanspatial frequency of the image swaths can be motivated by variousfactors such as a sub-scan size of each of the image swaths for example.

In this example embodiment, each image feature in each of the first andsecond sets of image features 60A and 60B comprises a sub-scan sizeequal to 64 pixels which corresponds to a contiguous arrangement of theimage features. In this example embodiment, each of the other imagefeature patterns 50 shown in FIG. 3A is also an interleaved imagefeature pattern with similar spatial characteristics.

In step 220, a contrast between imaged and non-imaged regions of therecording media 17 is adjusted. For example, various chemical processingsteps can be employed to remove undesired regions of the imagemodifiable surface of the recording media 17 to adjust the contrast.Contrast can be adjusted by separating a donor element from a receiverelement in a thermal transfer process. Adjusting contrast between theimaged and non-image regions of recording media 17 can be used toenhance an optical density difference between the first set of imagefeatures 60A and the second set of image features 60B. It is to be notedthat block 220 is outlined in broken lines to identify it as optionalsince the adjustment of contrast need not be required in all recordingmedia. For example, some recording media 17 work in an ablative fashionwhere the unwanted regions are removed by the imaging process. In thiscase, the imaging and contrast enhancement are achieved simultaneouslyalthough it is usually necessary to provide a debris collection systemto draw the ablated materials away from the recording media 17.

In step 230, data is generated from the imaged recording media 17. Inthis example embodiment of the invention, scanner 40 is employed togenerate data 47. As schematically represented in FIG. 4, scanner 40 isemployed to scan over the imaged recording media 17 generally along ascanning direction (i.e. the Y direction). In this example embodiment,the imaged recording media 17 is oriented within scanner 40 such that asub-scan direction employed during the formation of calibration image 19is aligned with the Y direction. In this particular example embodiment,each of the image feature patterns 50 comprises elongate image featuresthat extend along a first direction and scanner 40 is operated to scanacross the imaged recording media 17 along a second direction (i.e. theY direction) that intersects the first direction in a substantiallyorthogonal manner. Scanner 40 can include, or be modified to include,various guide mechanisms to facilitate the scanning of imaged recordingmedia 17 along a desired direction. In this example embodiment, scanner40 generates a two dimensional (2D) matrix 45 of data 47. In particular,the data 47 is regularly arranged in a plurality of data columns 46numbering M and a plurality of data rows 48 numbering N. In this exampleembodiment, each of the data rows 48 correspond to the scanningdirection (i.e. the Y direction) while each of the data columns 46correspond to arrangement directions of sensor array 42 in scanner 40(i.e. the X direction). It is understood that the number of cellsrepresenting data 47 in matrix 45 shown in FIG. 4 is limited forclarity. The number of cells that would form matrix 45 would be relatedto the scanning resolutions of scanner 40 along the X and Y directions.

The sampling rate of scanner 40 along the scanning direction (i.e. the Ydirection scanning rate) has a significant effect of a subsequentanalysis of the data 47 in the frequency domain. In one exampleembodiment, it is desired that the spatial frequency of each of thefirst and second sets of image features 60A and 60B be whollyrepresented by an integer factor of the scanner sampling spatialfrequency. In this example embodiment, the sub-scan spatial frequency ofthe image features in each of the first and second sets of imagefeatures 60A and 60B is selected to equal a non-integer multiple of asub-scan spatial frequency of the image swaths. Additionally, thesub-scan spatial frequency of the image features in each of the firstand second sets of image features 60A and 60B is selected such that thesampling spatial frequency employed by scanner 40 during the scanning isequal to an integer multiple of the sub-scan spatial frequency of theimage features in each of the first and second sets of image features60A and 60B. In this specific example embodiment, the sub-scan spatialfrequency of the image features in each of the first and second sets ofimage features 60A and 60B is 1 cycle per 128 pixels or 18.75 cycles perinch for a 2400 DPI image pixel resolution. The scanning resolution ofscanner 40 along the Y scanning direction is 300 DPI which provides asampling spatial frequency along the scanning direction of 300 cyclesper inch. Accordingly, the sampling spatial frequency along the scanningdirection of scanner 40 is 16 times the sub-scan spatial frequency ofthe image features in each of the first and second sets of imagefeatures 60A and 60B. This means that every 16 samples of scanner 40will correspond to 1 complete cycle of the image features in each of thecorresponding first and second sets of image features 60A and 60B.

Data 47 in the frequency domain is finite and is therefore separatedinto frequency bins. If a particular targeted frequency fits perfectlyinto a bin it will yield a maximum amplitude. If the targeted frequencyis not so aligned, deviations in the strength of the amplitude willarise. Additionally, noise is created in the frequency spectrum when aperiodic signal is cut part way through. Accordingly, it is preferredthat the frequency that is being analyzed fit into the data in each datarow 48 an integer number of times. In some example embodiments of theinvention, scanner 40 is operated such that each sensor element ofscanner 40 takes a first integer number of samples while scanning acrossthe overall width of an image feature pattern 50. One, or both of thescanning resolution and the spatial frequency of the image features ineach of the first and second sets of image features 60A and 60B isvaried to cause a product of the first integer number and the samplingspatial period of scanner 40 to equal a product of a second integernumber and the sub-scan spatial period (i.e. the inverse of the sub-scanspatial frequency) of the of the first and second sets of image features60A and 60B. For example, in a previously described embodiment, thesub-scan spatial frequency of the image features in each of the firstand second sets of image features 60A and 60B was 1 cycle per 128 pixelsor 18.75 cycles per inch. Accordingly, each of the first and second setsof image features 60A and 60B has a sub-scan spatial period of 0.0533inches. If the scanning resolution of scanner 40 along the Y scanningdirection was changed from 300 DPI to 200 DPI, the scanner samplingspatial frequency would no longer be equal to an integer multiple of thesub-scan spatial frequency of the image features in each of the firstand second sets of image features 60A and 60B. Nonetheless, a suitablesubsequent analysis of data 47 in the frequency domain can beaccomplished since every 3 of the sub-scan spatial periods (i.e. 0.0533inches) of the image features in each of the first and second sets ofimage features 60A and 60B is equal to 32 of the sampling spatialperiods (i.e. 0.005 inches) employed by scanner 40. In these exampleembodiments, a first integer multiple of the sampling spatial frequencyemployed by scanner 40 during the scanning is equal to a second integermultiple of the sub-scan spatial frequency of the image features in eachof the first and second sets of image features 60A and 60B. In thiscontext, the “integer multiple of a value” can include integer multiplesof the value that are equal to value or greater.

Some, or all, of the sub-scan spatial frequency of the image features,the sub-scan spatial frequency of the image swaths and the samplingspatial frequency of the employed scanner 40 can be varied in various inembodiments of the present invention. In some particular exampleembodiments, these varied entities can be controlled to cause thesub-scan spatial frequency of the image features in each of the firstand second sets of image features 60A and 60B to be equal to anon-integer factor or a non-integer multiple of the sub-scan spatialfrequency of the image swaths while a first integer multiple of thesampling spatial frequency employed by scanner 40 during the scanning isequal to a second integer multiple of the sub-scan spatial frequency ofthe image features in each of the first and second sets of imagefeatures 60A and 60B.

In step 240 the scanned data 47 is analyzed. In this example embodiment,the arrangements of data 47 representative of each of the image featurepatterns 50 are analyzed in the frequency domain. In this exampleembodiment, a Fast Fourier Transform (FFT) algorithm is employed toanalyze data 47. Other example embodiments of the invention can employother suitable algorithms to analyze data 47 in the frequency domain. Inthis example embodiment, the analysis can be performed by controller 30or the like.

FIG. 5 shows a block diagram representing an FFT algorithm 300 employedin an example embodiment of the invention. In step 310, a dataarrangement comprising data 47 in a portion of matrix 45 correspondingto a selected one the image feature patterns 50 is selected.

In step 320 a sum of squares is calculated for all the data 47 in thedata rows 48 and data columns 46 of portion of matrix 45 to determine avalue representing an overall density value for the selected one of theimage feature pattern 50.

A FFT is calculated in step 330 for each of the data rows 48 in theportion of matrix 45. In this example embodiment, each FFT will containM complex numbers, wherein each complex number represents a complexFourier transform amplitude within the spatial spectrum associated withthe corresponding data row 48. In this example embodiment, an equalnumber of complex numbers will be associated with each data row 48 andcorresponding complex numbers will be related to data 47 located in agiven data column 46.

In step 340 a magnitude value derived from each of the real andimaginary components of each of the complex numbers is squared. Step 340is performed for each of the FFT calculated for each data row 48.

In step 350 all the squared magnitude values derived from each data row48 and corresponding to a given data column 46 are summed to provide asingle row of squared and summed magnitude values.

In step 360, squared and summed magnitude values determined in step 350are normalized with the value calculated in step 320 to provide a finalrow of values that represents the frequency domain for the portion ofthe matrix 45 corresponding to the selected image feature pattern 50.

The FFT algorithm 300 is repeated for each portion of matrix 45corresponding to a given one of the image feature patterns 50. Eachportion of the matrix 45 is thus analyzed in the frequency domain toprovide a quantified value representative of banding created bydifferences in optical density among the interleaved image features in acorresponding image feature pattern 50 that is formed in accordance witha particular imaging parameter value (i.e. a focus value in this case).In this regard, each quantified value is a member of a group ofquantified values determined from the plurality of image featurepatterns 50.

FIG. 6 shows an example of plot in the frequency domain of the imagefeature pattern corresponding to the −3 micron focus offset value. Theplot in FIG. 6 shows a predominate peak 70 which is related to theintensity of the banding in the image feature pattern 50 correspondingto the −3 focus offset value. The intensity of the banding can berepresented by a quantified value which in this case is approximately5.5 in the FFT magnitude scale. It should be noted that very littlenoise is present in the plot shown in FIG. 6. An appropriate selectionof one or more of the sub-scan spatial frequency of the image featuresin each of the first and second sets of each image feature pattern 50,the sub-scan spatial frequency of the image swaths and the samplingspatial frequency employed by scanner 40 can be used to reduce noiselevels in similar plots in the frequency domain. In some exampleembodiments, data 47 is analyzed in the frequency domain at a frequencyvalue corresponding to the sub-scan spatial frequency of the imagefeatures in each of the first and second sets of each image featurepattern 50. In other example embodiments, data 47 is analyzed in thefrequency domain at a frequency value corresponding to a harmonic of thesub-scan spatial frequency of the image features in each of the firstand second sets of each image feature pattern 50.

In step 250 of method 200, the imaging parameter is adjusted at least inpart from the quantified value derived in step 240. FIG. 7 shows adistribution of various quantified values determined for each of aplurality of different focus offset values according to an exampleembodiment of the invention. Each of the quantified values is showncorrelated to a corresponding image parameter value which in this caseis an overall focus value. Each of the parameter values is equal to anaverage of the plurality of parameter values used to form the differentinterleaved sets of image features corresponding to each of the imagefeature patterns 50. The FIG. 7 plot shows the individual quantifiedvalues as well as a line “FIT” which is a mathematical curve fit to theplotted quantified values. In this example embodiment, the curve “FIT”that is applied is a second order polynomial. The present inventors havealso used other more involved relationships including 6th orderpolynomials, but have found that these relationships are typically notnecessary for this particular case.

The distribution of quantified values and the curve “FIT” show that thebanding intensity progressively increases as a focus offset increases ordecreases from a value of +9 microns. Accordingly, the focus offsetvalue of +9 microns corresponds to an optimum set-point for the focusimaging parameter. The FIG. 7 plot indicates that there appears to belittle difference between the measured optical densities correspondingto each of the bounding parameter values used to represent the +9 micronfocus offset value. In this example embodiment of the invention, a focusparameter associated with recording apparatus 10 is set to +9 micronsfor a subsequent imaging. In various example embodiments of theinvention, the imaging parameter may be adjusted in accordance with theidentification of a minimum value among a distribution of the determinedquantified values. In other example embodiments of the invention, theimaging parameter can be adjusted in accordance with inflection point ina mathematical curve fitted throughout a distribution of the quantifiedvalues.

It is to be noted that the “FIT” curve in the FIG. 7 plot dips below 0at a focus offset value of +9 microns. This is a result of the curvefitting exercise only and not the actual quantified values generated inthe frequency domain. The FIG. 7 plot also shows a focus offsetdistribution ranging from −3 microns to +23 microns whereas the imagefeature patterns 50 shown in FIG. 3A corresponded to a range of −9microns to +9 microns. If the quantified values determined from analysisof the image pattern features 50 of FIG. 3A were plotted, an operatormay not be able to positively ascertain an optimum focus value since allthe values are generally declining in magnitude. Accordingly, the FIG. 7plot corresponds to a second imaging of another recording media 17formed with image feature patterns 50 having a focus offset distributionshifted in the positive direction from those shown in FIG. 3A.

Other imaging parameters can be adjusted in accordance with the presentinvention. FIG. 8 shows a plot of quantified values determined infrequency domain for an imaging parameter related to a power of aradiation source within recording head 16. In this example embodiment, arecording media 17 was again imaged with a number of image featurepatterns, each of the image feature patterns corresponding to aparticular power value. Each of the image feature patterns is formed byinterleaving the image features in a first pattern of image featureswith the image features in a second pattern of the image features. Theimage features in each of the first and second patterns are formed inaccordance with different power values which average to equal theparticular power level represented in the corresponding image featurepattern. In various example embodiments, the spread between the boundingpower levels and/or the spread between the power levels represented byeach of the image feature patterns can be related to a particularrecording media 17 that is to be imaged.

In one example embodiment, a spread between the power levels representedby each of the image feature patterns on the order of 6% from theoverall power level of a first one of the image feature patterns can beemployed with good results. For example the first image feature patterncan correspond to 4.250 W. Six percent of 4.250 W is 0.255 W andtherefore the series of the image feature patterns would correspond tothe following series of power levels: 4.250 W, 4.505 W, 4.760 W, 5.015W, etc. In this case the spread between the bounding power levels (i.e.the interleaved power values) representative of the power levelcorresponding a particular image feature pattern is also selected to be±0.255 W. Accordingly, the image feature pattern corresponding to the4.250 W power level would include a first set of interleaved imagefeatures formed at 3.995 W and a second set of interleaved imagefeatures formed at 4.505 W. In a similar manner, the image featurepattern corresponding to the 4.505 W power level would include a firstset of interleaved image features formed at 4.250 W and a second set ofinterleaved image features formed at 4.760 W.

The FIG. 8 plot shows a number of quantified values determined in thefrequency domain from data generated from a scanning of the imagefeature patterns formed on the recording media 17. The FIG. 8 plot showsthat at underexposed powers the banding intensity is high as illustratedby the first few data points. The FIG. 8 plot additionally shows that asthe level of exposure is increased with increasing powers, the bandingintensity reduces and then plateaus. In this example embodiment, a setpoint for the power imaging parameter is determined by generating a bestfit first line 72 through the “plateau” region of the plotted quantifiedvalues and a best fit second line 74 through the quantified valuescorresponding to the underexposed regions of the plot. The intersectionpoint 76 between first line 72 and second line 74 represents the lowestexposure point of the recording media 17. From this a multiplier can beused to achieve a power set point.

In the example embodiment corresponding to the FIG. 8 plot, each of theimage feature patterns is produced while media support 12 is rotatedwith a common rotational speed. Since the exposure of recording media 17is related to this rotational speed, the determined power set-point mayneed to be recalculated if different imaging conditions that may requirechanges in this speed are required in the future.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the scope of theinvention.

Parts List

-   10 recording apparatus-   12 media support-   13 cylindrical surface-   16 recording head-   17 recording media-   18 carriage-   19 calibration image-   20 support-   21 radiation beam-   22 motion system-   23 recording channels-   25 registration features-   28 clamps-   30 controller-   32 guide system-   33 transmission member-   35 auto-focus system-   36 secondary laser source-   37 image data-   38 position sensitive detector-   40 scanner-   42 sensor array-   45 matrix-   46 data column-   47 data-   48 data row-   50 image feature patterns-   50A image feature pattern-   60A first set of image features-   60B second set of image features-   70 peak-   72 best fit first line-   74 best fit second line-   76 intersection-   100 imaging and diagnostics system-   200 method-   210 form calibration image on recording media-   220 adjust contrast between imaged and non-imaged regions-   230 generate data from image recording media-   240 analyze scanned data to determine a quantified value    representative of banding-   250 adjust imaging parameter based at least on the quantified value-   300 Fast Fourier Transform (FFT) algorithm-   310 select portion of scanned data matrix corresponding to one of    the image feature patterns-   320 calculate sum of squares for data in matrix portion-   330 calculate FFT for each data row in matrix portion-   340 derive a series of magnitude values for each FFT-   350 square each of the magnitude values and sum squared values    corresponding to a given data column-   360 normalize squared and summed magnitude levels-   MSA main-scan axis-   SSA sub-scan axis-   X direction-   Y direction-   M number-   N number

1. A method for adjusting an imaging parameter, comprising: operating a recording head to form a regular pattern of image swaths while forming an image on a recording media; operating the recording head to form a regular pattern of image features on the recording media, wherein the regular pattern of image features comprises a first set of image features that is formed while the imaging parameter is set to a first predetermined value and a second set of image features that is formed while the imaging parameter is set to a second predetermined value that is different from the first predetermined value, and wherein the image features in each of the first set of image features and the second set of image features are arranged on the recording media with a sub-scan spatial frequency that is equal to a non-integer multiple of a sub-scan spatial frequency of the image swaths in the regular pattern of image swaths; providing a scanner adapted to generate data while scanning over the regular pattern of image features formed on the recording media, wherein a first integer multiple of a sampling spatial frequency employed by the scanner during the scanning is equal to a second integer multiple of the sub-scan spatial frequency of each of the first set of image features and the second set of image features; analyzing the data to determine a quantified value representative of banding between the first set of image features and the second set of image features; and adjusting the imaging parameter based at least on the quantified value.
 2. A method according to claim 1, comprising operating the recording head to interleave image features in the first set of image features with image features in the second set of image features on the recording media.
 3. A method according to claim 2, wherein each of the first set of image features and the second set of image features is formed during a different scan of the recording head over the recording media.
 4. A method according to claim 2, comprising operating the recording head to concurrently forming at least one image feature in the first set of image features with at least one image feature in the second set of image features on the recording media.
 5. A method according to claim 2, wherein each image feature in the first set of image features is contiguously arranged with an image feature in the second set of image features on the recording media.
 6. A method according to claim 2, wherein the imaging parameter is an intensity of a radiation beam emitted by the recording head.
 7. A method according to claim 2, wherein the imaging parameter is a focus of a radiation beam emitted by the recording head.
 8. A method according to claim 2, wherein the imaging parameter is a power of a source of radiation in the recording head.
 9. A method according to claim 2, wherein analyzing the data to determine the quantified value comprises analyzing the data in the frequency domain.
 10. A method according to claim 9, comprising analyzing the data in the frequency domain at a frequency value corresponding to the sub-scan spatial frequency of each of the first set of image features and the second set of image features.
 11. A method according to claim 10, wherein the quantified value corresponds to the frequency value.
 12. A method according to claim 9, comprising analyzing the data in the frequency domain at a frequency value corresponding to a harmonic of the sub-scan spatial frequency of each of the first set of image features and the second set of image features.
 13. A method according to claim 2, wherein the regular pattern of image features is one a plurality of regular patterns of image features formed on the recording media, wherein each of the regular patterns of image features corresponds to a different set of imaging parameter values, and the method comprises: generating a plurality of data arrangements, each of the data arrangements being generated from a different one of the regular patterns of image features formed on the recording media; analyzing each data arrangement to determine a member within a group of quantified values, wherein each member within the group of quantified values is representative of banding in a corresponding one of the regular patterns of image features; and adjusting the imaging parameter based at least on the group of quantified values.
 14. A method according to claim 13, comprising adjusting the imaging parameter based at least on a minimum value determined from the group of the quantified values.
 15. A method according to claim 13, comprising adjusting the imaging parameter based at least on an inflection point in a mathematical curve derived from a distribution of the members of the group of quantified values.
 16. A method according to claim 2, wherein each image feature in the regular pattern of image features is an elongate image feature extending along a first direction and the data is generated by operating the scanner to scan over the recording media along a second direction that intersects the first direction.
 17. A method according to claim 2, comprising adjusting a contrast between an imaged region of the recording media and an un-imaged region of the recording media prior to generating the data from the regular pattern of image features.
 18. A method for generating data while scanning over an interleaved pattern of image features formed on recording media by a recording apparatus, the method comprising: operating a recording head of the recording apparatus to form a regular pattern of image swaths while imaging the recording media; operating the recording head to form a first regular pattern of image features on recording media; operating the recording head to form a second regular pattern of image features on the recording media; interleaving image features of the first regular pattern of image features with image features of the second regular pattern of image features to form the interleaved pattern of image features on the recording media; operating a scanner to generate the data while scanning over the interleaved pattern of image features formed on the recording media; and adjusting at least one of a sub-scan spatial frequency of the image swaths in the regular pattern of image swaths, a sub-scan spatial frequency of each of the first regular pattern of image features and the second regular pattern of image features, and a sampling spatial frequency of the scanner to cause one of the sub-scan spatial frequency of the image swaths in the regular pattern of image swaths and the sub-scan spatial frequency of each of the first regular pattern of image features and the second regular pattern of image features to be equal to a non-integer multiple of the other of the sub-scan spatial frequency of the image swaths in the regular pattern of image swaths and the sub-scan spatial frequency of each of the first regular pattern of image features and the second regular pattern of image features, and to cause a first integer multiple of the sampling spatial frequency employed by the scanner during the scanning to be equal to a second integer multiple of the sub-scan spatial frequency of each of the first regular pattern of image features and the second regular pattern of image features.
 19. A method according to claim 18, comprising forming each image feature in the first regular pattern of image features while an imaging parameter of the recording apparatus is set to a first predetermined value and forming each image feature in the second regular pattern of image features while the imaging parameter is set to a second predetermined value that is different from the first predetermined value, wherein at least one of the first predetermined value and the second predetermined value is selected to cause an optical density difference between the image features in the first regular pattern of image features and the image features in the second regular pattern of image features.
 20. A method according to claim 19, comprising analyzing the data in the frequency domain to determine a quantified value representative of the optical density difference, and adjusting the imaging parameter based at least on the quantified value
 21. A method according to claim 20, comprising analyzing the data in the frequency domain at a frequency value corresponding to the sub-scan spatial frequency of each of the first regular pattern of image features and the second regular pattern of image features.
 22. A method according to claim 21, wherein the quantified value corresponds to the frequency value.
 23. A method according to claim 22, wherein each image feature in the first regular pattern of image features is contiguously arranged with an image feature in the second regular pattern of image features on the recording media.
 24. A method according to claim 22, wherein the imaging parameter is an intensity of a radiation beam emitted by the recording head.
 25. A method according to claim 22, wherein the imaging parameter is a focus of a radiation beam emitted by the recording head.
 26. A method according to claim 22, wherein the imaging parameter is a power of a source of radiation in the recording head.
 27. A method according to claim 20, comprising analyzing the data in the frequency domain at a frequency value corresponding to a harmonic of the sub-scan spatial frequency of each of the first regular pattern of image features and the second regular pattern of image features.
 28. A controller for adjusting an imaging parameter of recording apparatus comprising a media support adapted for receiving recording media and a recording head adapted for emitting radiation beams to form an image on the recording media; wherein the controller is configured to: operate the recording head to form a regular pattern of image swaths while imaging the recording media; operate the recording head to form an interleaved pattern of image features on the recording media, wherein the interleaved pattern of image features comprises a first set of image features formed while the imaging parameter is set to a first predetermined value and a second set of image features formed while the imaging parameter is set to a second predetermined value that is different from the first predetermined value, and wherein the image features in the first set of image features are interleaved with the image features in the second set of image features, and the image features in each of the first set of image features and the second set of image features are arranged on the recording media with a sub-scan spatial frequency that is equal to one of a non-integer multiple and a non-integer factor of a sub-scan spatial frequency of the image swaths in the regular pattern of image swaths; receive data generated by a scanner while scanning over the interleaved pattern of image features formed on the recording media, wherein a first integer multiple of a sampling spatial frequency employed by the scanner during the scanning is equal to a second integer multiple of the sub-scan spatial frequency of each of the first set of image features and the second set of image features; analyze the data in the frequency domain to determine a quantified value representative of an optical density difference between the first set of image features and the second set of image features; and adjust the imaging parameter based at least on the quantified value. 